The "shield sign" in two men with metastatic salivary duct carcinoma to the skin: Cutaneous metastases presenting as carcinoma hemorrhagiectoides

Background: Salivary duct carcinoma is an infrequent and highly aggressive cancer that rarely metastasizes to the skin. Inflammatory cutaneous metastatic carcinoma is characterized by tumor cells predominantly in dermal lymphatics (carcinoma erysipelatoides) or blood vessels (carcinoma telangiectoides). Purpose: The authors present a distinctive cutaneous distribution of skin metastases from a visceral malignancy that resembles a medieval knight's shield and introduce a third pattern of inflammatory cutaneous metastatic carcinoma - carcinoma hemorrhagiectoides - which has a distinctive clinical presentation and pathological correlation. Methods: The authors describe the clinical and pathological characteristics of an unusual pattern of cutaneous metastases in two men with rapidly progressive salivary duct carcinoma and summarize the relevant literature. Immunoperoxidase stains with antibodies to CD31 and D2-40 were used to define the endothelial-lined dermal vessels containing tumor metastases: lymph vessels (CD31+/D2-40+) and blood vessels (CD31+/D2-40-). Results: Salivary duct carcinoma-related cutaneous metastases presented as large, violaceous, confluent, hemorrhagic and erythematous, dermal plaques across the chest and from the neck to the abdomen, reminiscent of a medieval knight's shield in two men. Microscopic examination demonstrated not only extensive infiltration of the dermis by tumor cells, but also tumor-containing endothelial-lined vessels: lymphatics (1 patient) or lymphatics and blood vessels (1 patient). Red blood cells were also noted in the tumor-filled lymph vessels of both patients. Conclusion: Salivary duct carcinoma with cutaneous metastases is rare (five patients) and the most common skin sites of metastatic tumor were the neck and chest. In addition to carcinoma erysipelatoides and carcinoma telangiectoides, inflammatory cutaneous metastatic carcinoma also includes carcinoma hemorrhagiectoides (with metastatic tumor cells in dermal lymphatics, blood vessels, or both) in which the skin metastases clinically appear as purpuric violaceous indurated plaques and microscopically demonstrates moderate-to-extensive extravascular tumor infiltration in the dermis and hemorrhage of red blood cells into endothelial-lined lymph vessels. The distinctive pattern of cutaneous metastases in the patients described in this article, resembling a medieval knight's shield, has also been observed - albeit rarely - in patients with a primary malignancy of the parotid gland, thyroid, or unknown origin. Hence, the "shield sign" may be an uncommon presentation of tumors originating and/or metastasizing to the head and neck.